Once the sun sets, “they come up under the cover of darkness so they can eat in peace,” she says.ĭr. She explains that during the day, zooplankton avoid predation and save energy by slowing down metabolism in the dark, chilly waters of the deep ocean. Steinberg’s research focuses on the ecology of zooplankton. Steinberg adds, “It’s a long way to go for a little critter.”ĭr. Scaling their body size to that of a human and considering the viscosity of sea water, their trek is like a nightly marathon through pudding. At their largest, zooplankton are but a dozen or so millimeters. “It’s like walking 25 miles to breakfast every morning,” says Dr. In terms of biomass, their migration is the largest on the planet, and they make that trek each night. When it comes to sheer biomass and relative distance traveled however, birds, butterflies and grandparents have nothing on the zooplankton that make up the deep scattering layer. Using sound, or sonar, scientists discovered this migration was a global phenomenon, one that occurs across the world’s oceans, in estuaries and in fresh water lakes.Īnimal migrations call to mind the annual trips of birds, monarch butterflies, or old people: massive flocks seeking greener pastures or a warm respite from winter weather. “It wasn’t until the 1940s they realized how widespread it was, when they could detect this layer of migrating organisms with sound.” World War II era sonar first mapped the extent of the mysterious "deep scattering layer"-which simply turned out to hordes of zooplankton. “The Navy would have been aware of it, but there were no acoustics in the 1800s,” says Dr. What no one appreciated was the vast expanse of this nightly sojourn. Deborah Steinberg, Professor at the Virginia Institute of Marine Science. “We knew that something was going on at nighttime,” says Dr. The discovery goes back to the expeditions of the HMS Challenger in the late 1800s. As to whether or not these salty sea critters could still hide an enemy in their ranks? That remains open to interpretation.įor nearly two centuries oceanographers knew that zooplankton rose higher in the water column at night. Today, research on the migration of zooplankton is as important as ever because researchers now recognize the critical importance of these organisms in the global carbon cycle. During the war, the Navy funded covert research operatives aimed at discerning sea monkey from submarine. It's zooplankton. The deep scattering layer is a stampede of sea monkeys whose combined biomass renders their nightly trek to feed on phytoplankton near the surface the largest animal migration on the planet. This enigmatic “deep scattering layer”, so named for the way it deflects sonar pings, turned out to be slightly more innocuous than enemy camouflage. Navy's sonar, leading to the belief that enemy submarines might be able hide within it. This cloud-like specter is ubiquitous, and so dense that during World War II it confounded the U.S. Every night a mysterious layer rises from the murky depths of the ocean, as though the seafloor has suddenly become detached and is floating to the surface.
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